THE MULTISTEP REVERSIBLE REDUCTION OF 1,4,5,8-NAPHTHALENE TETRACARBOXYLIC ACID DIANHYDRIDE - AN ELECTROCHEMICAL STUDY

Voltammetric experiments on 1,4,5,8-naphthalene tetracarboxylic acid dianhydride (I) (A) at a glassy carbon electrode (GC) in dry dimethylformamide +0.1 M Et4NClO4 are presented. The one-electron reduction of A produces anion radical A-: A+e- ⇄ A-. Subsequent electron transfers (A- +e- ⇄ A2- and A-2+e- ⇄ A3-) give rise to persistent dianion A2- and radical trianion A3-, with standard potentials E10 = -0.28 V, E20 = -0.69 V and E30 = -2.42 V (SCE), respectively. The above data have been used to assign the (relative) electron-acceptor property of I, in terms of electron affinity (EA). and the equilibrium constants for some redox reactions involving A, A-, A2- and A3-. In the presence of excess RX = t-BuBr, the redox couple A-/A2- (E20) is replaced by a more positive one with E20 = - 0.55 V. Reversible interaction of A2- with 2 mol of RX/mol A2- is indicated. Nothing similar happens with RX = 1-bromoadamantane. The results of preparative electrolyses of A in the presence of t-BuBr using a mercury pool cathode are also reported. R'= t-Bu-radical-derived products, i.e. HgR2 and dimers, were found, but only if A2- was produced at rather negative potentials, albeit where RX is not reduced directly. Minor products of preparative electrolyses of A were anhydride-lactone (II) and a red product to which structure III was assigned. UV-visible spectra of A2- are also reported. © 1990.